1. Field of the Invention
The present invention generally relates to an apparatus and a method of processing bandwidth requirements in an asynchronous transfer mode (ATM) switch.
More particularly, the invention relates to an apparatus and method of processing bandwidth requirements in an ATM switch to solve the problem of efficiently allocating resources where a multiplexed stream of ATM cells are to be individually switched to different physical ports.
2. Description of the Related Art
ATM traffic is predominantly bursty data traffic, although speech traffic may be included. By its nature, bursty traffic requires high bandwidths for part of the time and little or no bandwidth at others. In order to efficiently use the bandwidth available, it is necessary to allocate the bandwidth using each source's mean bandwidth requirement and not peak bandwidth. If mean bandwidth allocation is used, the total peak bandwidth of all the sources may thus be greater than the pipe bandwidth available.
Data destined for a particular output port will enter the switch from many different input ports. The total instantaneous data rate across the switch may be greater than the output port can sustain, thus buffering and eventual loss of data due to buffer overflow may occur. To reduce this probability to an operationally acceptable level results in a low utilization of the switch which is unacceptable. A dynamic bandwidth allocation (DBA) protocol, described in co-pending, patent application GB 9322744.5 provides a method of allocating bandwidth by sending requests for bandwidth to the required output port and sending data only when bandwidth has been allocated by an acknowledgement message.
Handling statistically multiplexed bursty data services and handling multicasting traffic are probably two of the most complex tasks to perform in an ATM switch. Most multicasting solutions require an ATM switch core speedup, a copy network or usually both. These methods are inefficient and do not lend themselves to bursty traffic.
The dynamic bandwidth allocation (DBA) protocol was designed to encapsulate an ATM switch to offer statistical multiplexing of bursty data services by offering a fair method of sharing bandwidth between cells destined for different outputs and by storing in a queue data which cannot be transferred immediately across the switch. Multicast traffic may also utilize components of the DBA protocol, but a new approach must be used.